Fuel vapor control system with leak check

ABSTRACT

A fuel vapor control system has a controller that carries out a leak check processing after the engine is stopped. The controller includes a device that intermittently activates the controller itself or a part of the controller to sample an internal pressure of the fuel vapor passage. Then, after a predetermined time, the controller determines that whether the sampled values of the internal pressure indicate a leak or not by evaluating the sampled values. According to the arrangement, since at least a part of the controller is activated intermittently, the consumption of electricity can be reduced. The fuel vapor control system has a canister valve and a purge valve made of normally close type valves in order to reduce the consumption of electricity after the engine is stopped.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2001-266637filed on Sep. 4, 2001 the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel vapor control system thatprevents fuel vapor from being emitted to the atmosphere, specificallythe fuel vapor control system having a controller for performing a selfleak check.

2. Description of Related Art

The fuel vapor control system has a canister that contains an adsorbentfor adsorbing fuel vapor from a fuel tank during operation of a fuelconsuming device such as when an engine is not activated. The fuel vaporadsorbed in the canister is desorbed and purged into the engine when theengine is activated and the fuel vapor is consumed. In the fuel vaporcontrol system, a purge valve is disposed between the canister and anintake pipe of the engine in order to control a purge amount in anappropriate amount. Further, in order to control a communication betweenthe canister and the atmosphere, a canister valve is disposed betweenthe canister and the atmosphere.

In order to ensure the function of the fuel vapor control system, it isimportant to detect a leak on the fuel vapor control system in an earlystage. The leak may be detected by monitoring an internal pressure ofthe fuel vapor control system when the fuel vapor control system isclosed. For example, the internal pressure of the fuel vapor controlsystem may be represented by a gas pressure in the fuel tank, and takesan unexpected change if the system has a leak. The leak check can becarried out either when the engine is activated or when the engine isnot activated. However, the leak check should be carried out during atime when the fuel vapor control system is in a stable condition. Thestable condition may be obtained more frequently when the engine is notactivated.

U.S. Pat. No. 5,263,462 discloses the leak check apparatus and method inwhich the leak check procedure is carried out while the engine is notactivated.

Generally, the engine drives a generator to supply electricity to thefuel vapor control system and a battery. Therefore, if the leak check iscarried out while the engine is not activated, the battery alonesupplies power to the fuel vapor control system. As a result, thebattery may over discharge electricity while executing the leak check.

Further, in order to improve an accuracy of the leak check, a period oftime for the leak check procedure should be extended as long aspossible. However, since a capacity of the battery is limited, it isdifficult to obtain such a longer period of time for the leak check.

Further, in order to maintain the fuel vapor control system in a closedcondition during the leak check procedure, the valves disposed in thefuel vapor control system also consumes the electricity of the battery.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a fuel vapor controlsystem that is capable of reducing the consumption of electricity forcarrying out the leak check.

It is an object of the present invention to provide a fuel vapor controlsystem that is capable of extending a period of time for the leak checkthat is carried out while the engine is not activated.

According to a first aspect of the present invention, a leak check iscarried out after the engine is stopped. During the leak check, the fuelvapor passage is closed as a closed chamber. In the fuel vapor passage,the internal pressure will be changed as the temperature of the fuelvapor is changed after the engine is stopped. The internal pressure ofthe fuel vapor passage demonstrates an existence of the leak or not. Theinternal pressure is sampled intermittently. Specifically, theintermittent sampling is carried out by activating a component forsampling the internal pressure. Therefore, the component can bedeactivated between the sampling timings. It is possible to reduce theconsumption of electricity.

According to the present invention, it is possible to monitor theinternal pressure for a long period of time with small powerconsumption. Therefore it is possible to keep electricity of the battery(i.e. maintain battery life).

According to another aspect of the present invention, the fuel vaporpassage is closed by at least one valve that is capable of maintaining aclosed condition without activation. Therefore, it is possible to reducethe consumption of electricity for activating the valve during the leakcheck.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments will be appreciated, as well asmethods of operation and the function of the related parts, from a studyof the following detailed description, the appended claims, and thedrawings, all of which form a part of this application. In the drawings:

FIG. 1 is a block diagram of a fuel vapor control system for a vehicleaccording to a first embodiment of the present invention;

FIG. 2 is a flow chart showing a leak check process according to thefirst embodiment of the present invention;

FIG. 3 is a time chart showing signals in the fuel vapor control systemduring the leak check process according to the first embodiment of thepresent invention;

FIG. 4 is a flow chart showing a leak check process according to asecond embodiment of the present invention; and

FIG. 5 is a time chart showing signals in the fuel vapor control systemduring the leak check process according to the second embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 to 3 show a first embodiment of a fuel vapor control system withleak check, which implements the present invention.

Referring to FIG. 1, the fuel vapor control system is disposed on avehicle such as a car having an internal combustion engine 1a. Theengine 1a has an intake passage 1b, and drives a generator 1c forsupplying power to the fuel vapor control system and for charging abattery 1d. The fuel vapor control system has components of a fuel vaporpassage and components of an electronic control system.

The fuel vapor passage has a fuel tank 11 that contains gasoline for aninternal combustion engine for a vehicle. An upper space of the fueltank 11 is connected to a first end of a canister 13 via a vapor conduit12. The canister 13 contains adsorbent such as activated carbon pellets13a. The adsorbent adsorbs fuel vapor from the fuel tank 11 during theengine is not activated. The canister 13 has a conduit on a second endthereof. The conduit communicates with the atmosphere. A canister valve14 is disposed on the conduit. The fuel vapor is introduced into thecanister 13 when the canister valve 14 opens the conduit. The canistervalve 14 is an electromagnetic valve and is a normally close type valve.The canister valve 14 is capable of maintaining a closed conditionduring current is not supplied. The canister valve 14 opens the conduitduring current is supplied. A relief valve 28 is disposed in parallel tothe canister valve 14. The relief valve 28 defines an upper limitpressure in the fuel vapor passage. Another relief valve 29 is alsodisposed in parallel to the canister valve 14. The relief valve 29defines a lower limit pressure in the fuel vapor passage.

The first end of the canister 13 is communicated with the intake passage1b of the engine via a purge conduit 15. The intake passage 1b ismaintained at a negative pressure during the engine is activated andoperated in a certain condition. Therefore, the fuel vapor adsorbed inthe canister 13 can be purged from the canister 13 and be introducedinto the intake passage 1b when the engine is activated. A purge valve16 is disposed on the purge conduit 15. The purge valve 16 controls apurge amount that is a flow amount through the purge conduit 15. Thepurge valve 16 is an electromagnetic valve and is a normally close typevalve. Further, an electromagnetic actuator of the purge valve 16 is alinear control actuator that is capable of operating an opening degreeof the purge valve 16 in accordance with a duty ratio of current.

The main components of the fuel vapor passage provide a closed chamberisolated from the atmosphere when both of the valves 14 and 16 areclosed. The main components include the fuel tank 11, the vapor conduit12, the canister 13, a part of the canister conduit and a part of thepurge conduit 15. Therefore, the fuel vapor passage is in a closedcondition when both of the canister valve 14 and the purge valve 16 areclosed. In this embodiment, a closing means of the fuel vapor passage isprovided by the valves 14 and 16. The components included in the closedchamber may be changed in accordance with a leak check requirement. Forexample, if a leak check for the fuel tank 11 alone is required, anothervalve may be disposed on the vapor conduit 12 for defining a closedchamber including the fuel tank 11 and a part of the vapor conduit 12.

The canister valve 14 and the purge valve 16 are also components of theelectronic control system of the fuel vapor control system. Theelectronic control system further includes a pressure sensor 17 that isdisposed on an upper portion of the fuel tank 11. The fuel tank 11 is apart of the fuel vapor passage which can be brought into a closedcondition by the valves 14 and 16. Therefore, the pressure sensor 17detects an internal pressure Pa of the fuel vapor passage. A fuel levelsensor 18 is also disposed on the fuel tank 11. The fuel level sensor 18detects a fuel level in the fuel tank 11. A fuel temperature sensor 26is disposed in the fuel tank 11. The fuel temperature sensor 26 detectsthe fuel temperature Tf of the fuel in the fuel tank 11. A watertemperature sensor 19 for detecting a water temperature Tw of a coolingwater of the engine and a intake air temperature sensor 20 for detectingan air temperature in the intake passage of the engine are disposed onthe engine.

An engine control unit (ECU) 21 is provided as a controller. The ECU 21inputs signals from the sensors 17, 18, 19, 20 and 26. The ECU 21 has amicroprocessor and peripheral devices including ROM, RAM, and I/O. TheECU 21 executes a fuel injection amount control, an ignition timingcontrol, a purge control and a leak check. In the purge control, the ECU21 controls the purge valve 16 so that the engine maintains appropriatecondition even the fuel vapor is purged from the canister 13 andintroduced into the intake passage 1b. In the leak check, the ECU 21monitors the internal pressure of the fuel vapor passage and determineswhether a leak exists or not.

The ECU 21 is powered by the battery id mounted on the vehicle. A mainrelay 22 is disposed between the battery 1d and the ECU 21. The mainrelay 22 has a relay contact 22a and a coil 22b. The coil 22b iscontrolled by the ECU 21. An ignition switch 23 is connected to the ECU21 to obtain a key switch signal indicative of an activation of theengine. The ECU 21 has a driver block 21a for driving the coil 22b inresponse to the ignition switch 23. The driver block 21a turns on thecoil 22b during the ignition switch 23 is turned on. The main relay 22supplies power to the sensors 17, 18, and 26 to activate them when theECU 21 is activated. The ignition switch 23 supplies power to thecanister valve 14 and the purge valve 16. Therefore, the valves 14 and16 are deactivated during the time that engine is not activated. The ECU21 has a back-up power source 24 and a soak timer 25. The back-up powersource 24 is a small capacity battery that is able to activate the soaktimer 25. The soak timer 25 measures an elapsed time from a turning offof the ignition switch 23. That is, the soak timer 25 measures anelapsed time from the engine is deactivated. The soak timer 25intermittently turns on the coil 22b with a predetermined interval. Thesoak timer 25 also obtains a signal indicative of the elapsed time tothe ECU 21 when the ECU 21 is activated by turning on the main relay 22.The soak timer 25 has a timer block 25a and a driver block 25b. Thetimer block 25a measures the elapsed time and obtains an intermittenttrigger signal. The driver block 25b drives the coil 22b in response tothe intermittent trigger signal. The soak timer 25 provides a powercontrol block. The driver blocks 21a and 25b and the timer block 25a maybe provided by hardware components or software components. A lamp 27 isconnected to the ECU 21. The lamp 27 is activated as a warning indicatorwhen the leak is detected.

The ECU 21 executes the leak check in accordance with a flowchartillustrated in FIG. 2. The ECU 21 executes a program corresponding tothe flowchart in response to a turning on of the relay 22. The flowchartin FIG. 2 is started every turning on of the relay 22. For example, whenthe driver turns on the ignition switch 23, the relay 22 is turned bythe driver block 21a and the ECU 21 starts a processing of the leakcheck. Further, after the engine is deactivated, the relay 22 isintermittently turned on by the driver block 25b and the ECU 21 starts aprocessing of the leak check.

The ECU 21 checks the soak timer 25 whether it is a leak check periodafter deactivating the engine or not in a step 101. The soak timer 25measures the elapsed time from an engine deactivation. Therefore, if theroutine is started in response to the ignition switch 23, the routinebranches to “No” and finishes the processing. On the other hand, if theroutine is started in response to the soak timer 25, the routine maybranches to a step 102. Moreover, if the leak check period is elapsed,the routine branches to “No”,

In the step 102, the ECU 21 determines whether a leak check condition issatisfied or not. In the step 102, the ECU 21 determines a prohibitionor permission of the leak check based on a parameter indicative of acondition of fuel vapor in the fuel tank. For example, in thisembodiment, the ECU 21 evaluates the fuel temperature Tf in the fueltank 11. If the fuel temperature Tf is higher than a predeterminedthreshold value, the ECU 21 determines the leak check condition issatisfied and proceeds to a step 103. If the fuel temperature Tf is nothigher than the predetermined threshold value, the ECU 21 skips thefollowing steps. If the fuel temperature Tf is not higher than thethreshold value, an internal pressure of the fuel vapor passage may notclearly indicate an existence of the leak. On the contrary, if the fueltemperature Tf is higher than the threshold value, the internal pressureof the fuel vapor passage will be changed in accordance with a change ofthe fuel temperature Tf after the engine is stopped and will demonstratea significant difference indicative of the existence of the leak.Therefore, if an accurate leak check is not expected due to low fueltemperature, the ECU 21 skips the leak check processing. The fueltemperature Tf may be replaceable with a parameter that correlates withthe fuel temperature. For example, a driving history of the vehiclebefore stopping the engine (driving time, or driving distance) or anoperating condition of the engine (cooling water temperature Tw) can beused. For example, if the driving time is longer than a predeterminedthreshold, or if the driving distance is longer than a predeterminedthreshold, the ECU 21 determines the leak check condition is satisfied.

In the step 103, the ECU 21 inputs the internal pressure Pa from thepressure sensor 17. The step 103 is executed only when the ignitionswitch 23 is turned off, therefore, the valves 14 and 16 are closed dueto no supply of drive current. Therefore, the internal pressure Padetected in the step 103 indicates the internal pressure of the fuelvapor passage under a closed condition.

In a step 104, it is determined that whether or not the internalpressure Pa is higher than a maximum pressure Pamax. If the internalpressure Pa is higher than the maximum pressure Pamax, the value of themaximum pressure Pamax is renewed by the present value of the internalpressure Pa in a step 105. If the internal pressure Pa is not higherthan the maximum pressure Pamax, it is determined that whether or notthe internal pressure Pa is lower than a minimum pressure Pamin in astep 106. If the internal pressure Pa is lower than the minimum pressurePamin, the value of the minimum pressure Pamin is renewed by the presentvalue of the internal pressure Pa in a step 107. The steps 104 to 107provide a maximum pressure learning block and a minimum pressurelearning block. Further, the steps 103 to 107 provide a sampling blockfor sampling the internal pressure Pa with a predetermined intervaldefined by the soak timer 25.

In a step 108, the ECU 21 checks the soak timer 25 again. If the elapsedtime measured by the soak timer 25 reaches to a predetermined leak checkperiod TC, the ECU 21 proceeds to a steps 109 to 113 which provide aleak check block. If the soak timer 25 has not yet reached to thepredetermined leak check period TC, the ECU 21 proceeds to a step 114.In the step 114, the ECU 21 turns off the relay 22 and wait until nextactivation by the soak timer 25.

In a step 109, the ECU 21 sets a threshold value f1(L). The thresholdvalue f1(L) may be set by looking up a map defined by a parameter suchas the fuel level L. The threshold value f1(L) may be obtained by amathematical formula. The fuel level L is considered in determining thethreshold value, because a pressure difference between the maximumpressure Pamax and the minimum pressure Pamin is influenced by the fuellevel L.

In a step 110, it is determined that whether or not the pressuredifference (Pamax−Pamin) is greater than the threshold value f1(L). Ifthe pressure difference (Pamax−Pamin) is greater than the thresholdvalue f1(L), the ECU 21 determines that no leak is detected in a step111 because the internal pressure Pa has been changed significantlyafter deactivating the engine. On the contrary, if the pressuredifference (Pamax−Pamin) is not greater than the threshold value f1(L),the ECU 21 determines that a leak is detected in a step 112, turns onthe lamp 27 and stores a leak code indicative of an existence of theleak in a step 113. Then, the ECU 21 turns off the relay 22 in the step114 to complete the sampling processing and the leak check processing.

FIG. 3 shows a time chart showing an operation of the first embodiment.The ignition switch 23 is turned off at t1. The valves 14 and 16 closesthe fuel vapor passage in response to the ignition switch 23. Theinternal pressure Pa is increased due to a high fuel temperature Tf andthe closed condition of the fuel vapor passage. Then, the internalpressure Pa is gradually decreased as the fuel temperature Tf isdecreased and is condensed into liquid due to a temperature decrease.The internal pressure Pa saturates in a certain pressure. During theleak check (sampling) period TC, the ECU 21 samples the internalpressure Pa in response to the intermittent operation of the relay 22.Downward arrows in FIG. 3 show sampling timings for the internalpressure Pa. The sampling processing is completed at t2, and the leakcheck processing is executed at t2. If the fuel vapor passage has aleak, the internal pressure Pa saturates in the atmospheric pressure (0)due to the leak. However, if the fuel vapor passage has no leak, theinternal pressure Pa fluctuates widely due to the temperature changeafter deactivating the engine. Therefore, the pressure difference(Pamax−Pamin) demonstrates the leak or not.

In this embodiment, most parts of the ECU 21 are not activated betweenthe sampling timings. Therefore it is possible to reduce the consumptionof electricity of the battery 1d.

Alternatively, the leak may be detected based on the maximum pressurePamax because the maximum pressure Pamax demonstrates a significantdifference between no leak and the existence of the leak. Further, theleak may be detected based on the minimum pressure Pamin alone.

Further, the leak may be detected based on an accumulated value of theinternal pressure Pa. FIGS. 4 and 5 show a second embodiment of thepresent invention, which detects the leak based on the accumulated valueof the internal pressure Pa.

Referring to FIG. 4, the same or similar steps as the first embodimentare indicated by the same reference numbers in order to avoid repeatdescription. In the second embodiment, a step 104a is executed insteadof the steps 104 to 107. In the step 104a, the accumulated value Ptotalis calculated by summing an absolute value of the internal pressure Pa.Therefore, the accumulated value Ptotal reflects an amount offluctuation of the internal pressure with respect to the atmosphericpressure (0). In the second embodiment, a step 109a and a step 110a areexecuted instead of the steps 109 and 110 respectively. In the step109a, a threshold value f2(L) is set based on a map or a mathematicalformula. In the step 110a, it is determined that whether or not theaccumulated value Ptotal is greater than the threshold value f2(L). Ifthe accumulated value Ptotal is greater than the threshold value f2(L),the ECU 21 determines that the fuel vapor passage has no leak. On thecontrary, if the accumulated value Ptotal is not greater than thethreshold value f2(L), the ECU 21 determines that the fuel vapor passagehas a certain amount of leak and proceeds to the step 113.

FIG. 5 shows an operation of the second embodiment. The accumulatedvalue Ptotal is saturated quickly in a small value due to a saturationof the internal pressure Pa into the atmospheric pressure (0) when thefuel vapor passage has a leak.

According to the second embodiment, since the leak check is executedbased on the accumulated value, it is possible to reflect a time factoror history of fluctuation of the internal pressure into the leak check.As a result, it is possible to improve the accuracy of the leak check.

The sampling interval TI is set in a constant in the first and secondembodiment, it is advantageous to simplify the processing of the ECU 21.However, the sampling interval TI may be set variable in order toimprove the accuracy or in order to decrease number of samples. Forexample, the sampling interval TI may be varied in accordance with theelapsed time from deactivating the engine, a changing rate of theinternal pressure Pa or a parameter correlates to them. For example, arelatively shorter interval may be used in a beginning period of theleak check period TC, because the internal pressure Pa varies quickly inthe beginning period as shown in FIG. 3. Then, a relatively longerinterval is used in order to decrease number of samples. In the case ofthe variable interval arrangement, it is possible to detect the maximumpressure accurately. It is also possible to avoid increase of number ofsamples.

The leak check period (sampling period) TC may be variable in accordancewith the fuel temperature or a parameter that correlates to the fueltemperature. For example, a driving history of the vehicle such as adriving time or a driving distance may be used as the parameter.Moreover, an engine operating condition such as the water temperature Twmay be used as the parameter. The leak check period TC may be variablein order to set an appropriate period according to an amount of vapor.

A normally open type valve may be used as the canister valve 14. In thiscase, the ECU 21 activates the canister valve 14 to close the conduitduring the leak check period TC. However, the consumption of electricityis still reduced due to the intermittent activation of the most parts ofthe ECU 21.

Further, the canister valve 14 and the relief valves 28 and 29 may bereplaced with a power saving type valve which needs activation only whenswitching valve conditions between open and close. For example, thepower saving type valve has a permanent magnet for keeping an opencondition or a close condition without activation, a coil for switchingthe condition from open to close and a coil for switching the conditionfrom close to open. In this case, the ECU 21 activates the power savingtype valve to close the conduit when the engine is stopped. Then, theECU 21 activates the power saving type valve to open the conduit whenthe leak check processing is completed.

Further, the step 108 may be removed in order to obtain a result of theleak check in an early stage. In this case, the leak check processing(steps 109-113, or steps 109a-113) is carried out in every samplingtimings. Therefore, if the detected value reaches to the thresholdvalue, the ECU 21 can determine no leak before an elapse of the leakcheck period TC. It is possible to reduce the consumption of electricityfurther.

Although the present invention has been described in connection with thepreferred embodiments thereof with reference to the accompanyingdrawings, it is to be noted that various changes and modifications willbe apparent to those skilled in the art. Such changes and modificationsare to be understood as being included within the scope of the presentinvention as defined in the appended claims.

1. A fuel vapor control system for a fuel supply system of an engine,comprising: means for detecting an internal pressure of a fuel vaporpassage including a fuel tank; means for closing the fuel vapor passageduring a leak check period in which a leak check is carried out when theengine is not activated; means, activated intermittently in the leakcheck period, for sampling the internal pressure intermittently inresponse to the activation so that the means for sampling consumeselectrical power when activated to perform the sampling and does notconsume electrical power when deactivated between sampling timings; andmeans for determining a leak or not based on the sampled values of theinternal pressure sampled by the sampling means.
 2. The fuel vaporcontrol system according to claim 1, wherein the sampling means isintermittently supplied the electrical power from a battery so that thebattery supplies electrical power to the sampling means when thesampling means is activated and does not supply electrical power to thesampling means when the sampling means is deactivated.
 3. The fuel vaporcontrol system according to claim 1, wherein the determining meansdetermines the leak or not based on a difference between a maximumpressure of the sampled values and a minimum pressure of the sampledvalues.
 4. The fuel vapor control system according to claim 3, whereinthe determining means determines the leak when the difference is smallerthan a predetermined value.
 5. The fuel vapor control system accordingto claim 1, wherein the determining means determines the leak or notbased on a maximum pressure of the sampled values.
 6. The fuel vaporcontrol system according to claim 5, wherein the determining meansdetermines the leak when the maximum pressure is smaller than apredetermined value.
 7. The fuel vapor control system according to claim1, wherein the determining means determines a leak or not based on anaccumulated value of the sampled values.
 8. The fuel vapor controlsystem according to claim 7, wherein the accumulated value is calculatedby accumulating absolute values of the sampled values.
 9. The fuel vaporcontrol system according to claim 1, wherein the closing means includes:a normally close type valve which is capable of maintaining a closedcondition without activation; and a relief valve which defines an upperlimit pressure in the fuel vapor passage.
 10. The fuel vapor controlsystem according to claim 1, further comprising: a canister that adsorbsfuel vapor from the fuel tank, wherein the closing means includes: apurge valve disposed between the canister and an intake passage of theengine, the purge valve being capable of maintaining a closed conditionwithout activation; and a canister valve disposed between the canisterand the atmosphere, the canister valve being capable of maintaining aclosed condition without activation.
 11. The fuel vapor control systemaccording to claim 1, wherein the sampling means varies a samplinginterval in accordance with at least one of an elapsed time of the leakcheck, a changing rate of the internal pressure and a parametercorrelating to the elapsed time or the changing rate.
 12. The fuel vaporcontrol system according to claim 11, wherein the sampling interval isset relatively shorter in a beginning of the leak check than that in anending of the leak check.
 13. The fuel vapor control system according toclaim 1, further comprising means for determining a prohibition orpermission of the leak check based on a parameter indicative of acondition of fuel vapor in the fuel tank.
 14. The fuel vapor controlsystem according to claim 13, wherein the parameter is a fueltemperature or a driving history of a vehicle that is indicative of thecondition of fuel vapor in which the internal pressure clearly shows theleak or not.
 15. A fuel vapor control system for a fuel supply system ofan engine, comprising: a valve that closes a passage to define a closedchamber including a part of the fuel vapor passage; a pressure sensordisposed on the closed chamber to detect an internal pressure of theclosed chamber; a controller that inputs a signal from the pressuresensor and operates the valve in a closed condition when a leak check iscarried out when an engine is not activated, wherein the controllerincludes: a power control block that intermittently turns on powersupply when the leak check is carried out; a sampling block that isintermittently activated by being supplied power from the power controlblock and samples the internal pressure detected by the pressure sensorin response to an activation and that is deactivated by not beingsupplied power from the power control block between sampling timings;and a leak check block that determines a leak or not based on values ofthe internal pressure sampled by the sampling block.
 16. The fuel vaporcontrol system according to claim 15, wherein the power control blockintermittently turns on power of the controller, and the valve iscapable of maintaining a closed condition when the controller is notsupplied power.
 17. The fuel vapor control system according to claim 15,wherein the controller is activated from an off condition, in which thepower is not supplied, when the leak check is carried out.
 18. The fuelvapor control system according to claim 1, wherein the sampling means isintermittently activated from an off condition, in which the power isnot supplied, during the leak check period.
 19. A method of controllingfuel vapor in a fuel supply system of an engine, the method comprising:detecting an internal pressure of a fuel vapor passage including a fueltank; closing the fuel vapor passage during a leak check period in whicha leak check is carried out when the engine is not activated; sampling,using a sampling device, the internal pressure intermittently inresponse to intermittent activation of the sampling device during theleak check period so that the sampling device consumes electrical powerwhen activated to perform the sampling and does not consume electricalpower when deactivated between sampling timings; and determining a leakor not based on the sampled values of the internal pressure sampled bythe sampling device.
 20. The method according to claim 19, wherein thesampling device is intermittently supplied the electrical power from abattery so that the battery supplies electrical power to the samplingdevice when the sampling device is activated and does not supplyelectrical power to the sampling device when the sampling device isdeactivated.
 21. The method according to claim 19, wherein determiningthe leak or not is based on a difference between a maximum pressure ofthe sampled values and a minimum pressure of the sampled values.
 22. Themethod according to claim 21, wherein the determining comprisesdetermining that the leak is present when the difference is smaller thana predetermined value.
 23. The method according to claim 19, whereindetermining the leak or not is based on a maximum pressure of thesampled values.
 24. The method according to claim 23, wherein thedetermining comprises determining that the leak is present when themaximum pressure is smaller than a predetermined value.
 25. The methodaccording to claim 19, wherein determining the leak or not is based onan accumulated value of the sampled values.
 26. The method according toclaim 25, wherein the accumulated value is calculated by accumulatingabsolute values of the sampled values.
 27. The method according to claim19, wherein closing the fuel vapor passage is accomplished by a normallyclose type valve which is capable of maintaining a closed conditionwithout activation, and a relief valve which defines an upper limitpressure in the fuel vapor passage.
 28. The method according to claim19, further comprising; absorbing fuel vapor from the fuel tank in acanister, and wherein closing the fuel vapor passage includes: disposinga purge valve between the canister and an intake passage of the engine,the purge valve being capable of maintaining a closed condition withoutactivation; and disposing a canister valve between the canister and theatmosphere, the canister valve being capable of maintaining a closedcondition without activation.
 29. The method according to claim 19,wherein the sampling includes varying a sampling interval in accordancewith at least one of an elapsed time of the leak check, a changing rateof the internal pressure and a parameter correlating to the elapsed timeor the changing rate.
 30. The method according to claim 29, wherein thesampling interval is set relatively shorter in a beginning of the leakcheck than that in an ending of the leak check.
 31. The method accordingto claim 19, further comprising determining a prohibition or permissionof the leak check based on a parameter indicative of a condition of fuelvapor in the fuel tank.
 32. The method according to claim 31, whereinthe parameter is a fuel temperature or a driving history of a vehiclethat is indicative of the condition of fuel vapor in which the internalpressure clearly shows the leak or not.
 33. A fuel vapor control systemfor a fuel supply system of an engine, comprising: means for closing afuel vapor passage during a leak check period in which a leak check iscarried out when the engine is not activated; means for activating ameans for sampling, intermittently in the leak check period, thatconsumes electrical power when activated and does not consume electricalpower when deactivated, and that is used for the leak check; and meansfor determining whether a leak exists by monitoring the means forsampling.
 34. The fuel vapor control system according to claim 33,wherein the means for sampling is a pressure sensor that detects apressure in the fuel tank.
 35. The fuel vapor control system accordingto claim 34, wherein the determining means determines whether a leakexists by monitoring the pressure in the fuel tank detected by thepressure sensor.
 36. A method of controlling fuel vapor in a fuel supplysystem of an engine, the method comprising: closing a fuel vapor passageduring a leak check period in which a leak check is carried out when theengine is not activated: activating a sampling device, intermittently inthe leak check period, that consumes electrical power when activated andthat is used for the leak check; and determining whether a leak existsby monitoring the sampling device.
 37. A method of controlling fuelvapor in a fuel supply system of an engine, the method comprising:closing a fuel vapor passage during a leak check period in which a leakcheck is performed while the engine is off; supplying power to asampling device for the leak check intermittently in the leak checkperiod so that the sampling device is activated intermittently;monitoring the component; and determining whether a leak exists based onthe result of monitoring the sampling device.